Telescopic booms having extension and retraction systems employing hydraulic cylinder and cables have been proposed. For instance, in U.S. Pat. No. 4,133,411, dated Jan. 9, 1979, an extension and retraction mechanism for a three section boom is disclosed utilizing an internally disposed hydraulic cylinder connected between a stationary base boom section and an intermediate telescopic boom section with a cable connection located interiorly of the boom and having opposite ends anchored to opposite ends of the base section with the cable reeved around sheaves on the movable end of the hydraulic cylinder and a base end of the intermediate boom section with a cable attachment to the base end of a fly section of the boom, whereby the fly section is the most extensible boom section.
U.S. Pat. No. 4,575,976, dated Mar. 18, 1976, discloses an extension and retraction system for a four section boom employing hydraulic cylinders and cables for extending and retracting the boom sections. A pair of hydraulic cylinders are serially connected between the proximate end of the base section, the distal end of the base section, and the distal end of the inner mid section. While the retraction cables are located within the base, inner mid, and outer mid sections, the extension cables are located exteriorly of the respective sections, thus being exposed to the elements and unprotected from damage or abrasion during operation.